Seismic exploration involves surveying subterranean geological media for hydrocarbon deposits. A survey typically involves deploying seismic sources and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological medium creating pressure changes and vibrations. Variations in physical properties of the geological medium give rise to changes in certain properties of the seismic waves, such as their direction of propagation and other properties.
Portions of the seismic waves reach the seismic sensors. Some seismic sensors are sensitive to pressure changes (e.g., hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy one type of sensor or both. In response to the detected seismic waves, the sensors generate corresponding electrical signals, known as traces, and record them in storage media as seismic data.
One goal of seismic exploration is drilling hazard prediction and mitigation. Such drilling hazards are present, for example, when a region of a porous material in a geological medium has an abnormally high fluid pressure. An abnormally high fluid pressure is often indicated by lower wave velocity (e.g., s-wave or p-wave velocity) than the trend corresponding to normal pressured fluid. Some conventional approaches use imaging velocity analysis of seismic data (e.g., tomographic inversion) for drilling hazard prediction and mitigation. Seismic migrations of various types (e.g., Kirchhoff prestack depth migration, reverse-time migration) are currently the methods of choice for seismic imaging. Migration velocity analyses oftentimes adjust the seismic imaging velocity iteratively, by maximizing imaging focusing or aligning imaging gathers (i.e., minimizing residual moveout, or image misalignment, in prestack imaging gathers). Unfortunately, these conventional methods of imaging velocity analysis (e.g., methods of creating a velocity model of a geological medium using seismic data collected from the region for best imaging) are not optimized for hazard prediction and do not yield sufficient resolution to predict drilling hazards that occur on smaller, laterally extended (e.g., three-dimensional), length-scales. Thus, hazards remain.